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优秀装饰器源码学习（一）：time ​

前言 ​

最近又温习了一遍TS装饰器，准备用装饰器改造一下自己的轮子

在改造之前，准备先学习一下优秀的装饰器开源库，站在巨人的肩膀上前行

根据一些博文的推荐，就选择了core-decorators

准备工作 ​

可将源码 clone到本地进行学习

也可直接利用github1s在线预览

搭建测试环境 ​

全局安装ts-node与typescript两个依赖

sh
npm install ts-node typescript -g
npm install ts-node typescript -g

初始化ts配置文件（tsconfig.json）

sh
tsc --init
tsc --init

将noImplicitAny,noImplicitThis设置为false，experimentalDecorators设置为true

json
{
  "compilerOptions": {
    /* Visit https://aka.ms/tsconfig.json to read more about this file */

    "target": "es5",                              
    "lib": ["ESNext","DOM"], 
    /* Strict Type-Checking Options */
    "strict": true,                                 /* Enable all strict type-checking options. */
    "noImplicitAny": false,                       
    "noImplicitThis": false,                      /* Raise error on 'this' expressions with an implied 'any' type. */
    "esModuleInterop": true,                        /* Enables emit interoperability between CommonJS and ES Modules via 
    /* Experimental Options */
    "experimentalDecorators": true,              /* Enables experimental support for ES7 decorators. */
    /* Advanced Options */
    "skipLibCheck": true,                           /* Skip type checking of declaration files. */
    "forceConsistentCasingInFileNames": true        /* Disallow inconsistently-cased references to the same file. */
  }
}
{
  "compilerOptions": {
    /* Visit https://aka.ms/tsconfig.json to read more about this file */

    "target": "es5",                              
    "lib": ["ESNext","DOM"], 
    /* Strict Type-Checking Options */
    "strict": true,                                 /* Enable all strict type-checking options. */
    "noImplicitAny": false,                       
    "noImplicitThis": false,                      /* Raise error on 'this' expressions with an implied 'any' type. */
    "esModuleInterop": true,                        /* Enables emit interoperability between CommonJS and ES Modules via 
    /* Experimental Options */
    "experimentalDecorators": true,              /* Enables experimental support for ES7 decorators. */
    /* Advanced Options */
    "skipLibCheck": true,                           /* Skip type checking of declaration files. */
    "forceConsistentCasingInFileNames": true        /* Disallow inconsistently-cased references to the same file. */
  }
}

编写示例测试

ts
function defaultValue(str:string){
    return function(target,property){
        target[property] = str
    }
}

class User {

    @defaultValue('666')
    private _name: string | undefined
    constructor(name?:string) {
        if(name){
            this._name = name
        }
    }
    get name(){
        return this._name
    }
}

const a = new User()

console.log(a.name); // 666
function defaultValue(str:string){
    return function(target,property){
        target[property] = str
    }
}

class User {

    @defaultValue('666')
    private _name: string | undefined
    constructor(name?:string) {
        if(name){
            this._name = name
        }
    }
    get name(){
        return this._name
    }
}

const a = new User()

console.log(a.name); // 666

运行,结果如上数的注释所示

ts
ts-node first.ts
ts-node first.ts

源码目录 ​

图片

简单数了一下大概有17个，咱一个个的挨着学，细细品

下面开始和大家一起学，由易到难

time ​

用于计算一个函数执行耗时

使用示例 ​

使用如下,通过一个简单的 @time 即可让函数执行完后打印执行时间

ts
import { time } from './../index'
class Test {
    @time()
    sayHello() {
        let i = 0
        while (i < 100000) {
            i++
        }
        console.log('success');
    }
}

const t = new Test()
t.sayHello()
import { time } from './../index'
class Test {
    @time()
    sayHello() {
        let i = 0
        while (i < 100000) {
            i++
        }
        console.log('success');
    }
}

const t = new Test()
t.sayHello()

执行效果 ​

图片

console.time实现 ​

计算程序的执行时间可以利用console.time与console.timeEnd实现

ts
console.time('label')
// ...code 
console.timeEnd('label') // 即可打印出执行耗时
console.time('label')
// ...code 
console.timeEnd('label') // 即可打印出执行耗时

源码中为避免环境不支持console.time/timeEnd，巧妙实现了一下，源码如下

ts
const labels = {}

// 替代console.time
const myTime = (label) => {
    // 记录开始时间
    labels[label] = new Date().getTime()
}

// 替代console.timeEnd
const myTimeEnd = (label) => {
    const timeNow = new Date().getTime();
    // 当前时间与开始时间做差
    const timeTaken = timeNow - labels[label];
    // 删除无用的标志
    delete labels[label];
    // 打印耗时
    console.log(`${label}: ${timeTaken}ms`);
}
const labels = {}

// 替代console.time
const myTime = (label) => {
    // 记录开始时间
    labels[label] = new Date().getTime()
}

// 替代console.timeEnd
const myTimeEnd = (label) => {
    const timeNow = new Date().getTime();
    // 当前时间与开始时间做差
    const timeTaken = timeNow - labels[label];
    // 删除无用的标志
    delete labels[label];
    // 打印耗时
    console.log(`${label}: ${timeTaken}ms`);
}

函数结构 ​

传入参数:

  • prefix:默认null
  • 自定义console:默认使用内建的console.time/timeEnd
ts
// 首先是console.time的polyfill
// 当没定义time与timeEnd的时候，利用labels变量实现类似的效果
const defaultConsole = {
    time: console.time ? console.time.bind(console) : myTime,
    timeEnd: console.timeEnd ? console.timeEnd.bind(console) : myTimeEnd
}
// 用于label生成
let count = 0

export default function time(prefix: null | string = null, console = defaultConsole) {
    return function (target, key, descriptor) {
        
    }
}
// 首先是console.time的polyfill
// 当没定义time与timeEnd的时候，利用labels变量实现类似的效果
const defaultConsole = {
    time: console.time ? console.time.bind(console) : myTime,
    timeEnd: console.timeEnd ? console.timeEnd.bind(console) : myTimeEnd
}
// 用于label生成
let count = 0

export default function time(prefix: null | string = null, console = defaultConsole) {
    return function (target, key, descriptor) {
        
    }
}

最终实现 ​

ts
let count = 0
export default function time(prefix: null | string = null, console = defaultConsole) {
    return function (target, key, descriptor) {
        const fn = descriptor.value
        // 如果没有传参
        // 使用构造函数的名称与装饰对象的属性名作为key
        if (prefix === null) {
            prefix = `${target.constructor.name}.${key}`;
        }

        // 校验装饰对象是否为函数
        if (typeof fn !== 'function') {
            throw new SyntaxError(`@time can only be used on functions, not: ${fn}`);
        }

        return {
            ...descriptor,
            value() {
                const label = `${prefix}-${count}`
                count++
                console.time(label)
                try {
                    return fn.apply(this, arguments)
                } finally {
                    console.timeEnd(label)
                }
            }
        }
    }
}
let count = 0
export default function time(prefix: null | string = null, console = defaultConsole) {
    return function (target, key, descriptor) {
        const fn = descriptor.value
        // 如果没有传参
        // 使用构造函数的名称与装饰对象的属性名作为key
        if (prefix === null) {
            prefix = `${target.constructor.name}.${key}`;
        }

        // 校验装饰对象是否为函数
        if (typeof fn !== 'function') {
            throw new SyntaxError(`@time can only be used on functions, not: ${fn}`);
        }

        return {
            ...descriptor,
            value() {
                const label = `${prefix}-${count}`
                count++
                console.time(label)
                try {
                    return fn.apply(this, arguments)
                } finally {
                    console.timeEnd(label)
                }
            }
        }
    }
}

未完待续 ​

本文主要介绍了测试环境的搭建，跟着源码一起重现了time函数

后续文章将直接对源码进行分析与学习

更新于: